Bug 1160148: Disable CRT use of FMA3 on non-AVX2 processors. r=froydnj

toolkit/xre/nsWindowsWMain.cpp

@@ -11,6 +11,8 @@
 #endif
 
 #include "nsUTF8Utils.h"
+#include <intrin.h>
+#include <math.h>
 
 #ifndef XRE_DONT_PROTECT_DLL_LOAD
 #include "nsSetDllDirectory.h"
@@ -88,6 +90,17 @@ int wmain(int argc, WCHAR **argv)
   WindowsCrtPatch::Init();
 #endif
 
+#if defined(_MSC_VER) && _MSC_VER < 1900 && defined(_M_X64)
+  // Disable CRT use of FMA3 on non-AVX2 processors because of bug 1160148
+  int cpuid0[4] = {0};
+  int cpuid7[4] = {0};
+  __cpuid(cpuid0, 0); // Get the maximum supported CPUID function
+  __cpuid(cpuid7, 7); // AVX2 is function 7, subfunction 0, EBX, bit 5
+  if (cpuid0[0] < 7 || !(cpuid7[1] & 0x20)) {
+    _set_FMA3_enable(0);
+  }
+#endif
+
 #ifndef XRE_DONT_PROTECT_DLL_LOAD
   mozilla::SanitizeEnvironmentVariables();
   SetDllDirectoryW(L"");